1. Field of the Application
The application relates to a semiconductor device and a method of fabricating the same, and more particularly to a nitride semiconductor light emitting diode (LED) and a method of fabricating the same.
2. Description of Related Art
Recently, the demands for photo-electric materials having high efficiency increase greatly with the population in photo-electric technology and related industries. The semiconductor compound material has gradually become the main stream in photo-electric materials for its advantages such as high light emitting efficiency, long life cycle, wide range for adjusting band gap, low cost, and so on. Herein, the nitride semiconductor material is suitable to be adopted as the material with the light emitting wavelengths of blue light to ultra-violet light, and can be applied in color displays, LEDs, high frequency electronic devices, semiconductor lasers, and the like. The nitride semiconductor material is especially adopted in the popular blue light LED devices and thus receives wide attention.
Conventional LED devices include an N-type doped nitride semiconductor layer, an active layer, a P-type doped nitride semiconductor layer, and two metal electrodes formed on a substrate sequentially. Moreover, the two metal electrodes are electrically connected to the N-type doped nitride semiconductor layer and the P-type doped semiconductor layer respectively. The active layer includes, for example, at least two quantum barrier layers and a quantum well located between the quantum barrier layers. A band gap of the quantum barrier layers has to be higher than a band gap of the quantum well to prevent a carrier from escaping after falling into the quantum well, thereby increasing the confinement of the carriers. Generally, the quantum well is fabricated with InxGa1-xN, where x ranges from 0 to 1. The quantum barrier layers are fabricated with materials having lattice constants similar to those of the quantum well (so as to alleviate the piezoelectric effect). Also, a suitable amount of aluminum (Al) is added so that the band gap of the quantum barrier layers is higher than that of the quantum well. For instance, the quantum barrier layers is fabricated with AlxGayIn1-x-yN, where x, y range from 0 to 1. However, the large addition of aluminum in the quantum barrier layers lowers the quality of lattices subsequently formed in the quantum wells, thereby resulting in pits. In addition, the large addition of aluminum in the quantum barrier layers increases current leakage and fails to effectively inhibit the piezoelectric effect and enhance the internal quantum efficiency (IQE).
A nitride semiconductor light emitting device is disclosed in U.S. Patent Publication No. US2008/0093619, where a quantum barrier layer in an active region thereof is a multilayer structure. The quantum barrier layer in the disclosure includes an InGaN layer, an AlInN layer, and an InGaN/GaN super-lattice structure. These structures are capable of forming a superior interface with the P-type doped nitride semiconductor layer and prevent the magnesium (Mg) in the P-type doped nitride semiconductor layer from diffusing into the active layer. In order for the quantum barrier layer containing AlInN and the quantum well to have a sufficient band gap, the aluminum content has to be greater than 15%. However, the above aluminum content does not guarantee a sufficient band gap. Furthermore, the large amount of the aluminum content can not reduce the piezoelectric effect between the quantum well and the quantum barrier layer effectively.